Bombardment map, Vimy Ridge, 4 April 1917. The dense network of German trenches in this sector was largely destroyed in the bombardment before the battle of Arras. By 9 April, the First Army found that there had been too much trench bombardment.

From "The infantry cannot do with a gun less": the place of the artillery in the British Expeditionary Force, 1914-1918 by Sanders Marble